Vibrating device and image equipment having the same

ABSTRACT

A vibrating device includes a drive unit configured to drive a vibrating member to produce vibration Z (x, y) at a dust-screening member, the vibration being expressed as follows:
 
 Z ( x,y )= W   mn ( x,y )·cos(γ)+ W   nm ( x,y )·sin(γ)
 
where Z (x, y) is vibration at a given point P (x, y) on the dust-screening member, m and n are positive integers including 0, indicating the order of natural vibration corresponding to a vibrational mode,
 
                   W   mn     ⁡     (     x   ,   y     )       =       sin   ⁡     (       n   ⁢           ⁢     π   ·   x       +     π   2       )       ·     sin   ⁡     (       m   ⁢           ⁢     π   ·   y       +     π   2       )           ,     
     ⁢         W     n   ⁢           ⁢   m       ⁡     (     x   ,   y     )       =       sin   ⁡     (       m   ⁢           ⁢     π   ·   x       +     π   2       )       ·     sin   ⁡     (       n   ⁢           ⁢     π   ·   y       +     π   2       )           ,   and         
γ is +π/4 or ranges from −π/8 to −π/4. A ratio between a first bending rigidity along the X-axis of at least the dust-screening member and vibrating member in the section orthogonal to the X-axis at the intersection of the X- and Y-axes, to a second bending rigidity along the Y-axis of at least the dust-screening member and vibrating member in the section orthogonal to the Y-axis at the intersection is 0.4 or more, but less than 1.0.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Applications No. 2008-335068, filed Dec. 26, 2008;and No. 2009-262657, filed Nov. 18, 2009, the entire contents of both ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to image equipment having image formingelements such as an image sensor element or a display element, and alsoto a vibrating device designed to vibrate the dust-screening member thatis arranged at the front of each image forming element of such an imageequipment.

2. Description of the Related Art

As image equipment having image forming elements, there is known animage acquisition apparatus that has an image sensor element configuredto produce a video signal corresponding to the light applied to itsphotoelectric conversion surface. Also known is an image projector thathas a display element, such as liquid crystal element, which displays animage on a screen. In recent years, image equipment having such imageforming elements have been remarkably improved in terms of imagequality. If dust adheres to the surface of the image forming elementsuch as the image sensor element or display element or to the surface ofthe transparent member (optical element) that is positioned in front ofthe image forming element, the image produced will have shadows of thedust particles. This makes a great problem.

For example, digital cameras of called “lens-exchangeable type” havebeen put to practical use, each comprising a camera body and aphotographic optical system removably attached to the camera body. Thelens-exchangeable digital camera is so designed that the user can usevarious kinds of photographic optical systems, by removing thephotographic optical system from the camera body and then attaching anyother desirable photographic optical system to the camera body. When thephotographic optical system is removed from the camera body, the dustfloating in the environment of the camera flows into the camera body,possibly adhering to the surface of the image sensor element or to thesurface of the transparent member (optical element), such as a lens,cover glass or the like, that is positioned in front of the image sensorelement. The camera body contains various mechanisms, such as a shutterand a diaphragm mechanism. As these mechanisms operate, they producedust, which may adhere to the surface of the image sensor element aswell.

Projectors have been put to practical use, too, each configured toenlarge an image displayed by a display element (e.g., CRT or liquidcrystal element) and project the image onto a screen so that theenlarged image may be viewed. In such a projector, too, dust may adhereto the surface of the display element or to the surface of thetransparent member (optical element), such as a lens, cover glass or thelike, that is positioned in front of the display element, and enlargedshadows of the dust particles may inevitably be projected to the screen.

Various types of mechanisms that remove dust from the surface of theimage forming element or the transparent member (optical element) thatis positioned in front of the image sensor element, provided in suchimage equipment have been developed.

In an electronic image acquisition apparatus disclosed in, for example,U.S. 2004/0169761 A1, a ring-shaped piezoelectric element (vibratingmember) is secured to the circumferential edge of a glass plat shapedlike a disc (dust-screening member). When a voltage of a prescribedfrequency is applied to the piezoelectric element, the glass plat shapedlike a disc undergoes a standing-wave, bending vibration having nodes atthe concentric circles around the center of the glass plat shaped like adisc. This vibration removes the dust from the glass disc. The vibration(vibrational mode 1) produced by the voltage of the prescribed frequencyis a standing wave having nodes at the concentric circles around thecenter of the disc. The dust particles at these nodes cannot be removed,because the amplitude of vibration at the nodes is small. In view ofthis, the glass plat shaped like a disc is vibrated at a differentfrequency, achieving a standing-wave vibration (vibrational mode 2) thathas nodes at concentric circles different from those at which the nodesof vibrational mode 1 are located. Thus, those parts of the glass disc,where the nodes lie in vibrational mode 1, are vibrated at largeamplitude.

Jpn. Pat. Appln. KOKAI Publication No. 2007-228246 discloses arectangular dust-screening member and piezoelectric elements secured tothe opposite sides of the dust-screening member, respectively. Thepiezoelectric elements produce vibration at a predetermined frequency,resonating the dust-screening member. Vibration is thereby achieved insuch mode that nodes extend parallel to the sides of the dust-screeningmember. Further, as in the mechanism of U.S. 2004/0169761 A1, thedust-screening member is made to resonate at a different frequency,accomplishing a standing-wave vibrational mode, in order to change theopposition of nodes. Any one of these vibrational modes achieves bendingvibration having nodes extending parallel to the sides of thedust-screening member.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda vibrating device comprising:

a dust-screening member which is shaped like a plate as a whole and hasat least one side that is symmetric to the X-axis that is a given axisof symmetry;

a vibrating member secured to the dust-screening member and configuredto produce, at the dust-screening member, vibration having a vibrationalamplitude perpendicular to a surface of the dust-screening member; and

a drive unit configured to drive the vibrating member to producevibration Z (x, y) at the dust-screening member, the vibration beingexpressed as follows:Z(x,y)=W _(mn)(x,y)·cos(γ)+W _(nm)(x,y)·sin(γ)where Z (x, y) is vibration at a given point P (x, y) on thedust-screening member; m and n are positive integers including 0,indicating the order of natural vibration corresponding to a vibrationalmode;

${{W_{mn}\left( {x,y} \right)} = {{\sin\left( {{n\;{\pi \cdot x}} + \frac{\pi}{2}} \right)} \cdot {\sin\left( {{m\;{\pi \cdot y}} + \frac{\pi}{2}} \right)}}};$${{W_{n\; m}\left( {x,y} \right)} = {{\sin\left( {{m\;{\pi\; \cdot x}} + \frac{\pi}{2}} \right)} \cdot {\sin\left( {{n\;{\pi \cdot y}} + \frac{\pi}{2}} \right)}}};{and}$

γ is +π/4 or ranges from −π/8 to −π/4; and

a ratio between a first bending rigidity along the X-axis of at leastthe dust-screening member and vibrating member in the section orthogonalto the X-axis at the intersection of the X- and Y-axes, to a secondbending rigidity along the Y-axis of at least the dust-screening memberand vibrating member in the section orthogonal to the Y-axis at theintersection is 0.4 or more, but less than 1.0, the Y-axis beingorthogonal to the X-axis in a virtual rectangle which has the same areaas the surface of the dust-screening member, and which has long sidesincluding the one side of the dust-screening member.

According to a second aspect of the present invention, there is providedan image equipment comprising:

an image forming element having an image surface on which an opticalimage is formed;

a dust-screening member which is shaped like a plate as a whole, has atleast one side that is symmetric to the X-axis that is a given axis ofsymmetry, and has a light-transmitting region at least flaring in aradial direction from the center, facing the image surface and spacedtherefrom by a predetermined distance;

a vibrating member configured to produce vibration having an amplitudeperpendicular to a surface of the dust-screening member, the vibratingmember being provided on the dust-screening member, outside thelight-transmitting region through which a light beam forming an opticalimage on the image surface passes;

a sealing structure for surrounding the image forming element and thedust-screening member, thereby providing a closed space in which theimage forming element and the dust-screening member that face eachother; and

a drive unit configured to drive the vibrating member to producevibration Z (x, y) at the dust-screening member, the vibration beingexpressed as follows:Z(x,y)=W _(mn)(x,y)·cos(γ)+W _(nm)(x,y)·sin(γ)where Z (x, y) is vibration at a given point P (x, y) on thedust-screening member; m and n are positive integers including 0,indicating the order of natural vibration corresponding to a vibrationalmode;

${{W_{mn}\left( {x,y} \right)} = {{\sin\left( {{n\;{\pi \cdot x}} + \frac{\pi}{2}} \right)} \cdot {\sin\left( {{m\;{\pi \cdot y}} + \frac{\pi}{2}} \right)}}};$${{w_{n\; m}\left( {x,y} \right)} = {{\sin\left( {{m\;{\pi \cdot x}} + \frac{\pi}{2}} \right)} \cdot {\sin\left( {{n\;{\pi \cdot y}} + \frac{\pi}{2}} \right)}}};{and}$

γ is +π/4 or ranges from −π/8 to −π/4, wherein

a ratio between a first bending rigidity along the X-axis of at leastthe dust-screening member and vibrating member in the section orthogonalto the X-axis at the intersection of the X- and Y-axes, to a secondbending rigidity along the Y-axis of at least the dust-screening memberand vibrating member in the section orthogonal to the Y-axis at theintersection is 0.4 or more, but less than 1.0, the Y-axis beingorthogonal to the X-axis in a virtual rectangle which has the same areaas the surface of the dust-screening member, and which has long sidesincluding the one side of the dust-screening member.

Advantages of the invention will be set forth in the description whichfollows, and in part will be obvious from the description, or may belearned by practice of the invention. Advantages of the invention may berealized and obtained by means of the instrumentalities and combinationsparticularly pointed out hereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a block diagram schematically showing an exemplary systemconfiguration, mainly electrical, of a lens-exchangeable, single-lensreflex electronic camera (digital camera) that is a first embodiment ofthe image equipment according to this invention;

FIG. 2A is a vertical side view of an image sensor element unit of thedigital camera, which includes a dust removal mechanism (or a sectionalview taken along line A-A shown in FIG. 2B);

FIG. 2B is a front view of the dust removal mechanism, as viewed fromthe lens side;

FIG. 3 is an exploded perspective view showing a major component(vibrator) of the dust removal mechanism;

FIG. 4A is a front view of a dust filter, explaining how the dust filteris vibrated;

FIG. 4B is a sectional view of the dust filter, taken along line B-Bshown in FIG. 4A;

FIG. 4C is a sectional view of the dust filter, taken along line C-Cshown in FIG. 4A;

FIG. 5 is a diagram explaining the length of the long sides and that ofthe short sides of the dust filter;

FIG. 6 is a diagram showing the relation the length ratio ofpiezoelectric elements and the vibration speed ratio of the center partof the dust filter shown in FIG. 4A;

FIG. 7 is a diagram showing the relation the bending rigidity ratio andthe vibration speed ratio of the center part of the dust filter shown inFIG. 4A;

FIG. 8 is a diagram explaining how the dust filter is vibrated in stillanother mode;

FIG. 9 is a front view of the dust filter vibrated in such a mode thatnode areas, where vibration hardly occurs, form a lattice pattern;

FIG. 10 is a diagram explaining the concept of vibrating the dustfilter;

FIG. 11 is a diagram showing another configuration the dust filter mayhave;

FIG. 12 is a diagram showing still another configuration the dust filtermay have;

FIG. 13 is a conceptual diagram of the dust filter, explaining thestanding wave that is produced in the dust filter;

FIG. 14A is a diagram showing an electric equivalent circuit that drivesthe vibrator at a frequency near the resonance frequency;

FIG. 14B is a diagram showing an electric equivalent circuit that drivesthe vibrator at the resonance frequency;

FIG. 15 is a circuit diagram schematically showing the configuration ofa dust filter control circuit;

FIG. 16 is a timing chart showing the signals output from the componentsof the dust filter control circuit;

FIG. 17A is the first part of a flowchart showing an exemplary camerasequence (main routine) performed by the microcomputer for controllingthe digital camera body according to the first embodiment;

FIG. 17B is the second part of the flowchart showing the exemplarycamera sequence (main routine);

FIG. 18 is a flowchart showing the operating sequence of “silentvibration” that is a subroutine shown in FIG. 17A;

FIG. 19 is a flowchart showing the operation sequence of the “displayprocess” performed at the same time Step S201 of “silent vibration,”i.e. subroutine (FIG. 18), is performed;

FIG. 20 is a flowchart showing the operating sequence of the “displayprocess” performed at the same time Step S203 of “silent vibration,”i.e., or subroutine (FIG. 18), is performed;

FIG. 21 is a flowchart showing the operating sequence of the “displayprocess” performed at the same time Step S205 of “silent vibration,”i.e., subroutine (FIG. 18), is performed;

FIG. 22 is a diagram showing the form of a resonance-frequency wavecontinuously supplied to vibrating members during silent vibration; and

FIG. 23 is a flowchart showing the operating sequence of “silentvibration,” i.e., subroutine in the operating sequence of the digitalcamera that is a second embodiment of the image equipment according tothe present invention.

DETAILED DESCRIPTION OF THE INVENTION

Best modes of practicing this invention will be described with referenceto the accompanying drawings.

First Embodiment

An image equipment according to this invention, which will beexemplified below in detail, has a dust removal mechanism for the imagesensor element unit that performs photoelectric conversion to produce animage signal. Here, a technique of improving the dust removal functionof, for example, an electronic camera (hereinafter called “camera” willbe explained. The first embodiment will be described, particularly inconnection with a lens-exchangeable, single-lens reflex electroniccamera (digital camera), with reference to FIGS. 1 to 2B.

First, the system configuration of a digital camera 10 according to thisembodiment will be described with reference to FIG. 1. The digitalcamera 10 has a system configuration that comprises body unit 100 usedas camera body, and a lens unit 200 used as an exchange lens, i.e., oneof accessory devices.

The lens unit 200 can be attached to and detached from the body unit 100via a lens mount (not shown) provided on the front of the body unit 100.The control of the lens unit 200 is performed by the lens-controlmicrocomputer (hereinafter called “Lucom”) 201 provided in the lens unit200. The control of the body unit 100 is performed by the body-controlmicrocomputer (hereinafter called “Bucom” 101 provided in the body unit100. By a communication connector 102, the Lucom 210 and the Bucom 101are electrically connected to each other, communicating with each other,while the lens unit 200 remains attached to the body unit 100. The Lucom201 is configured to cooperate, as subordinate unit, with the Bucom 101.

The lens unit 200 further has a photographic lens 202, a diaphragm 203,a lens drive mechanism 204, and a diaphragm drive mechanism 205. Thephotographic lens 202 is driven by a DC motor (not shown) that isprovided in the lens drive mechanism 204. The diaphragm 203 is driven bya stepping motor (not shown) that is provided in the diaphragm drivemechanism 205. The Lucom 201 controls these motors in accordance withthe instructions made by the Bucom 101.

In the body unit 100, a penta-prism 103, a screen 104, a quick returnmirror 105, an ocular lens 106, a sub-mirror 107, a shutter 108, an AFsensor unit 109, an AF sensor drive circuit 110, a mirror drivemechanism 111, a shutter cocking mechanism 112, a shutter controlcircuit 113, a photometry sensor 114, and a photometry circuit 115 arearranged as shown in FIG. 1. The penta-prism 103, the screen 104, thequick return mirror 105, the ocular lens 106, and the sub-mirror 107 aresingle-lens reflex components that constitute an optical system. Theshutter 108 is a focal plane shutter arranged on the photographicoptical axis. The AF sensor unit 109 receives a light beam reflected bythe sub-mirror 107 and detects the degree of defocusing.

The AF sensor drive circuit 110 controls and drives the AF sensor unit109. The mirror drive mechanism 111 controls and drives the quick returnmirror 105. The shutter cocking mechanism 112 biases the spring (notshown) that drives the front curtain and rear curtain of the shutter108. The shutter control circuit 113 controls the motions of the frontcurtain and rear curtain of the shutter 108. The photometry sensor 114detects the light beam coming from the penta-prism 103. The photometrycircuit 115 performs a photometry process on the basis of the light beamdetected by the photometry sensor 114.

In the body unit 100, an image acquisition unit 116 is further providedto perform photoelectric conversion on the image of an object, which haspassed through the above-mentioned optical system. The image acquisitionunit 116 is a unit composed of a CCD 117 that is an image sensor elementas an image forming element, an optical low-pass filter (LPF) 118 thatis arranged in front of the CCD 117, and a dust filter 119 that is adust-screening member. Thus, in this embodiment, a transparent glassplate (optical element) that has, at least at its transparent part, arefractive index different from that of air is used as the dust filter119. Nonetheless, the dust filter 119 is not limited to a glass plate(optical element). Any other member (optical element) that exists in theoptical path and can transmit light may be used instead. For example,the transparent glass plate (optical element) may be replaced by anoptical low-pass filter (LPF), an infrared-beam filter, a deflectionfilter, a half mirror, or the like. In this case, the frequency anddrive time pertaining to vibration and the position of a vibrationmember (later described) are set in accordance with the member (opticalelement). The CCD 117 is used as an image sensor element. Nonetheless,any other image sensor element, such as CMOS or the like, may be usedinstead.

As mentioned above, the dust filter 119 can be selected from variousdevices including an optical low-pass filter (LPF). However, thisembodiment will be described on the assumption that the dust filter is aglass plate (optical element).

To the circumferential edge of the dust filter 119, two piezoelectricelements 120 a and 120 b and two elastic members 121 (see FIG. 2B) areattached. The piezoelectric elements 120 a and 120 b have two electrodeseach. A dust filter control circuit 122, which is a drive unit, drivesthe piezoelectric elements 120 a and 120 b at the frequency determinedby the size and material of the dust filter 119. As the piezoelectricelements 120 a and 120 b vibrate, the dust filter 119 undergoes specificvibration. Dust can thereby be removed from the surface of the dustfilter 119. To the image acquisition unit 116, an anti-vibration unit isattached to compensate for the motion of the hand holding the digitalcamera 10.

The digital camera 10 according to this embodiment further has a CCDinterface circuit 123, a liquid crystal monitor 124, an SDRAM 125, aFlash ROM 126, and an image process controller 127, thereby to performnot only an electronic image acquisition function, but also anelectronic record/display function. The CCD interface circuit 123 isconnected to the CCD 117. The SDRAM 125 and the Flash ROM 126 functionas storage areas. The image process controller 127 uses the SDRAM 125and the Flash ROM 126, to process image data. A recording medium 128 isremovably connected by a communication connector (not shown) to the bodyunit 100 and can therefore communicate with the body unit 100. Therecording medium 128 is an external recording medium, such as one ofvarious memory cards or an external HDD, and records the image dataacquired by photography. As another storage area, a nonvolatile memory129, e.g., EEPROM, is provided and can be accessed from the Bucom 101.The nonvolatile memory 129 stores prescribed control parameters that arenecessary for the camera control.

To the Bucom 101, there are connected an operation display LCD 130, anoperation display LED 131, a camera operation switch 132, and a flashcontrol circuit 132. The operation display LCD 130 and the operationdisplay LED 131 display the operation state of the digital camera 10,informing the user of this operation state. The operation display LED131 or the operation display LED 131 has, for example, a display unitconfigured to display the vibration state of the dust filter 119 as longas the dust filter control circuit 122 keeps operating. The cameraoperation switch 132 is a group of switches including, for example, arelease switch, a mode changing switch, a power switch, which arenecessary for the user to operate the digital camera 10. The flashcontrol circuit 133 drives a flash tube 134.

In the body unit 100, a battery 135 used as power supply and apower-supply circuit 136 are further provided. The power-supply circuit136 converts the voltage of the battery 135 to a voltage required ineach circuit unit of the digital camera 10 and supplies the convertedvoltage to the each circuit unit. In the body unit 100, too, a voltagedetecting circuit (not shown) is provided, which detects a voltagechange at the time when a current is supplied from an external powersupply though a jack (not shown).

The components of the digital camera 10 configured as described aboveoperate as will be explained below. The image process controller 127controls the CCD interface circuit 123 in accordance with theinstructions coming from the Bucom 101, whereby image data is acquiredfrom the CCD 117. The image data is converted to a video signal by theimage process controller 127. The image represented by the video signalis displayed by the liquid crystal monitor 124. Viewing the imagedisplayed on the liquid crystal monitor 124, the user can confirm theimage photographed.

The SDRAM 125 is a memory for temporarily store the image data and isused as a work area in the process of converting the image data. Theimage data is held in the recording medium 128, for example, after ithas been converted to JPEG data.

The mirror drive mechanism 111 is a mechanism that drives the quickreturn mirror 105 between an up position and a down position. While thequick return mirror 105 stays at the down position, the light beamcoming from the photographic lens 202 is split into two beams. One beamis guide to the AF sensor unit 109, and the other beam is guided to thepenta-prism 103. The output from the AF sensor provided in the AF sensorunit 109 is transmitted via the AF sensor drive circuit 110 to the Bucom101. The Bucom 101 performs the distance measuring of the known type. Inthe meantime, a part of the light beam, which has passed through thepenta-prism 103, is guided to the photometry sensor 114 that isconnected to the photometry circuit 115. The photometry circuit 115performs photometry of the known type, on the basis of the amount oflight detected by the photometry sensor 114.

The image acquisition unit 116 that includes the CCD 117 will bedescribed with reference to FIGS. 2A and 2B. Note that the hatched partsshown in FIG. 2B show the shapes of members clearly, not to illustratingthe sections thereof.

As described above, the image acquisition unit 116 has the CCD 117, theoptical LPF 118, the dust filter 119, the piezoelectric elements 120 aand 120 b, and the elastic members 121. The CCD 117 is an image sensorelement that produces an image signal that corresponds to the lightapplied to its photoelectric conversion surface through the photographicoptical system. The optical LPF 118 is arranged at the photoelectricconversion surface of the CCD 117 and removes high-frequency componentsfrom the light beam coming from the object through the photographicoptical system. The dust filter 119 is a dust-screening member arrangedin front of the optical LPF 118 and facing the optical LPF 118, spacedapart therefrom by a predetermined distance. The piezoelectric elements120 a and 120 b are arranged on the circumferential edge of the dustfilter 119 and are vibrating members for applying specific vibration tothe dust filter 119. The elastic members 121 adjust the bending rigiditywith respect to the X- and Y-directions, in order to increase thevibrational amplitude of the dust filter 119.

As described above, the piezoelectric elements 120 a and 120 b arearranged on the edge parts of the dust filter 119. This means that thepiezoelectric elements 120 a and 120 b are fixed to the dust filter 119with adhesive, or may contact the dust filter 119. If the piezoelectricelements 120 a and 120 b are fixed to the dust filter 119 with adhesive,the bending rigidity of the vibrating system composed of thepiezoelectric elements 120 a and 120 b and the dust filter 119 will beadjusted. If the piezoelectric elements 120 a and 120 b contact the dustfilter 119, the bending rigidity of only the dust filter 119 will beadjusted.

The CCD chip 137 of the CCD 117 is mounted directly on a flexiblesubstrate 138 that is arranged on a fixed plate 139. From the ends ofthe flexible substrate 138, connection parts 140 a and 140 b extend.Connectors 141 a and 141 b are provided on a main circuit board 142. Theconnection parts 140 a and 140 b are connected to the connectors 141 aand 141 b, whereby the flexible substrate 138 is connected to the maincircuit board 142. The CCD 117 has a protection glass plate 143. Theprotection glass plate 143 is secured to the flexible substrate 138,with a spacer 144 interposed between it and the flexible substrate 138.

Between the CCD 117 and the optical LPF 118, a filter holding member 145made of elastic material is arranged on the front circumferential edgeof the CCD 117, at a position where it does not cover the effective areaof the photoelectric conversion surface of the CCD 117. The filterholding member 145 abuts on the optical LPF 118, at a part close to therear circumferential edge of the optical LPF 118. The filter holdingmember 145 functions as a sealing member that maintains the junctionbetween the CCD 117 and the optical LPF 118 almost airtight. A holder146 is provided, covering seals the CCD 117 and the optical LPF 118 inairtight fashion. The holder 146 has a rectangular opening 147 in a partthat is substantially central around the photographic optical axis. Theinner circumferential edge of the opening 147, which faces the dustfilter 119, has a stepped part 147 having an L-shaped cross section.Into the opening 147, the optical LPF 118 and the CCD 117 are fittedfrom the back. In this case, the front circumferential edge of theoptical LPF 118 contacts the stepped part 147 in a virtually airtightfashion. Thus, the optical LPF 118 is held by the stepped part 148 at aspecific position in the direction of the photographic optical axis. Theoptical LPF 118 is therefore prevented from slipping forwards from theholder 146. The level of airtight sealing between the CCD 117 and theoptical LPF 118 is sufficient to prevent dust from entering to form animage having shadows of dust particles. In other words, the sealinglevel need not be so high as to completely prevent the in-flow ofgasses.

On the front circumferential edge of the holder 146, a dust-filterholding unit 149 is provided, covering the entire front circumferentialedge of the holder 146. The dust-filter holding unit 149 is formed,surrounding the stepped part 148 and projecting forwards from thestepped part 148, in order to hold the dust filter 119 in front of theLPF 118 and to space the filter 119 from the stepped part 148 by apredetermined distance. The opening of the dust-filter holding unit 149serves as focusing-beam passing area 150. The dust filter 119 is shapedlike a polygonal plate as a whole (a square plate, in this embodiment).The dust filter 119 is supported on the dust-filter holding unit 149,pushed onto the dust-filter holding unit 149 by a pushing member 151which is constituted by an elastic body such as a leaf spring and hasone end fastened with screws 152 to the dust-filter holding unit 149.More specifically, a cushion member 153 made of vibration attenuatingmaterial, such as rubber or resin, is interposed between the pushingmember 151 and the dust filter 119. On the other hand, between the backof the dust filter 119 and the dust-filter holding unit 149, a cushionmember 154 is interposed, which is almost symmetric with respect to thephotographic optical axis and which is made of vibration-attenuatingmaterial such as rubber. The cushion members 153 and 154 hold the dustfilter 119, not to impede the vibration of the dust filter 119. The dustfilter 119 is positioned with respect to the Y-direction in the planethat is perpendicular to the optical axis, as that part of the pushingmember 151 which is bent in the Z-direction, receive a force through asupport member 155. On the other hand, the dust filter 119 is positionedwith respect to the X-direction in the plane that is perpendicular tothe optical axis, as a support part 156 provided on the holder 146receive a force through the support member 155, as is illustrated inFIG. 2B. The support member 155 is made of vibration-attenuatingmaterial such as rubber or resin, too, not to impede the vibration ofthe dust filter 119. The cushion members 153 and 154 may be located atnodes of the vibration of the dust filter 119, which will be describedlater. In this case, the vibration of the dust filter 119 will be almostimpeded. This can provide an efficient dust removal mechanism thatachieves vibration of large amplitude. Between the circumferential edgeof the dust filter 119 and the dust-filter holding unit 149, a seal 157having an annular lip part is arranged, defining an airtight spaceincluding an opening 147. The image acquisition unit 116 is thusconfigured as an airtight structure that has the holder 146 having adesired size and holding the CCD 117. The level of airtight sealingbetween the dust filter 119 and the dust-filter holding unit 149 issufficient to prevent dust from entering to form an image having shadowsof dust particles. The sealing level need not be so high as tocompletely prevent the in-flow of gasses.

As described above, the dust filter 119 is supported to the dust-filterholding unit 149 by the pushing member 151 via the cushion members 153and 154. Nonetheless, the dust filter 119 may be supported by the seal157, not by the cushion member 154 at least.

To the ends of the piezoelectric elements 120 a and 120 b, which arevibrating members, flexes 158 a and 158 b, i.e., flexible printedboards, are electrically connected. The flexes 158 a and 158 b input anelectric signal (later described) from the dust filter control circuit122 to the piezoelectric elements 120 a and 120 b, causing the elements120 a and 120 b to vibrate in a specific way. The flexes 158 a and 158 bare made of resin and cupper etc., and have flexibility. Therefore, theylittle attenuate the vibration of the piezoelectric elements 120 a and120 b. The flexes 158 a and 158 b are provided at positions where thevibrational amplitude is small (at the nodes of vibration, which will bedescribed later), and can therefore suppress the attenuation ofvibration. The piezoelectric elements 120 a and 120 b move relative tothe body unit 100 if the camera 10 has such a hand-motion compensatingmechanism as will be later described. Hence, if the dust filter controlcircuit 122 is held by a holding member formed integral with the bodyunit 100, the flexes 158 a and 158 b are deformed and displaced as thehand-motion compensating mechanism operates. In this case, the flexes158 a and 158 b effectively work because they are thin and flexible. Inthe present embodiment, the flexes 158 a and 158 b have a simpleconfiguration, extending from two positions. They are best fit for usein cameras having a hand-motion compensating mechanism.

The dust removed from the surface of the dust filter 119 falls onto thebottom of the body unit 100, by virtue of the vibration inertia and thegravity. In this embodiment, a base 159 is arranged right below the dustfilter 119, and a holding member 160 made of, for example, adhesivetape, is provided on the base 159. The holding member 160 reliably trapsthe dust fallen from the dust filter 119, preventing the dust frommoving back to the surface of the dust filter 119. That is, the dustfilter 119, which is a dust-screening member, is shaped like a plate andhas a focusing-beam passing area 150, i.e., light-transmitting partthrough which the light beam coming from the object passes. The dustfilter 119 is shaped symmetric with respect to one or both of the X- andY-axes that are two-dimensional virtual axes orthogonal to the axis ofthe light beam coming from the object. The X-axis 161 is parallel toopposite sides of the CCD 117, and the Y-axis is parallel to the otheropposite sides of the CCD 117. The CCD 117 is arranged on the opticalaxis and spaced apart from the dust filter 119 by a predetermineddistance. The CCD 117 converts the light beam coming from the objectthrough the light-transmitting part of the dust filter 119, into anelectrical signal. The piezoelectric elements 120 a and 120 b as thevibrating members are shaped like a plate, and are arranged,respectively, at the outer edges of the two sides of the dust filter119, which intersect with one of the X- and Y-axes 161 and 162. Thepiezoelectric elements 120 a and 120 b and vibrate the dust filter 119in a specific manner.

The elastic members 121 are arranged, respectively, at the outer edgesof the two sides of the dust filter 119, which intersect with the otherof the X-axis 161 and Y-axis 162. That is, the elastic members 121 arearranged at the two opposite sides of the dust filter 119, which areother than the sides at which the piezoelectric elements 120 a and 120 bare arranged.

The hand-motion compensating mechanism will be explained in brief. Asshown in FIG. 1, the hand-motion compensating mechanism is composed ofan X-axis gyro 163, a Y-axis gyro 164, a vibration control circuit 165,an X-axis actuator 166, a Y-axis actuator 167, an X-frame 168, a Y-frame169 (holder 146), a frame 170, a position sensor 171, and an actuatordrive circuit 172. The X-axis gyro 163 detects the angular velocity ofthe camera when the camera moves, rotating around the X axis. The Y-axisgyro 164 detects the angular velocity of the camera when the camerarotates around the Y axis. The vibration control circuit 165 calculatesa value by which to compensate the hand motion, from theangular-velocity signals output from the X-axis gyro 163 and Y-axis gyro164. In accordance with the hand-motion compensating value thuscalculated, the actuator drive circuit 172 moves the CCD 117 in theX-axis direction and Y-axis direction, which are first and seconddirections orthogonal to each other in the XY plane that isperpendicular to the photographic optical axis, thereby to compensatethe hand motion, if the photographic optical axis is taken as Z axis.More precisely, the X-axis actuator 166 drives the X-frame 168 in theX-axis direction upon receiving a drive signal from the actuator drivecircuit 172, and the Y-axis actuator 167 drives the Y-frame 169 in theY-axis direction upon receiving a drive signal from the actuator drivecircuit 172. That is, the X-axis actuator 166 and the Y-axis actuator167 are used as drive sources, the X-frame 168 and the Y-frame 169(holder 146) which holds the CCD 117 of the image acquisition unit 116are used as objects that are moved with respect to the frame 170. Notethat the X-axis actuator 166 and the Y-axis actuator 167 are eachcomposed of an electromagnetic motor, a feed screw mechanism, and thelike. Alternatively, each actuator may be a linear motor using a voicecoil motor, a linear piezoelectric motor or the like. The positionsensor 171 detects the position of the X-frame 168 and the position ofthe Y-frame 169. On the basis of the positions the position sensor 171have detected, the vibration control circuit 165 controls the actuatordrive circuit 172, which drives the X-axis actuator 166 and the Y-axisactuator 167. The position of the CCD 117 is thereby controlled.

The dust removal mechanism of the first embodiment will be described indetail, with reference to FIGS. 3 to 13. The dust filter 119 has atleast one side symmetric with respect to a certain symmetry axis, and isa glass plate (optical element) of a polygonal plate as a whole (asquare plate, in this embodiment). The dust filter 119 has a regionflaring in the radial direction from the center. This region forms atransparent part. Alternatively, the dust filter 119 may be D-shaped,formed by cutting a part of a circular plate, thus defining one side.Still alternatively, it may formed by cutting a square plate, having twoopposite sides accurately cut and having upper and lower sides. Theabove-mentioned fastening mechanism fastens the dust filter 119, withthe transparent part opposed to the front of the LPF 118 and spaced fromthe LPF 118 by a predetermined distance. To one surface of the dustfilter 119 (i.e., back of the filter 119, in this embodiment), thepiezoelectric elements 120 a and 120 b, which are vibrating members, aresecured at the upper and lower edges of the filter 119, by means ofadhesion using adhesive. The piezoelectric elements 120 a and 120 b,which are arranged on the dust filter 119, constitute a vibrator 173.The vibrator 173 undergoes resonance when a voltage of a prescribedfrequency is applied to the piezoelectric elements 120 a and 120 b. Theelastic members 121 are fixed, by adhesion or a similar means, to thosesides of the dust filter 119, at which the piezoelectric elements 120 aand 120 b are not arranged. The elastic members 121 adjust the bendingrigidities of the X- and Y-axial parts of the vibrator 173 having thepiezoelectric elements 120 a and 120 b, respectively, which are arrangedon the dust filter 119. The elastic members 121 therefore cause thevibrators 173 to vibrate in one of the vibrational modes shown in FIGS.4A to 4C. The vibrator 173, which has the piezoelectric elements 120 aand 120 b and the elastic members 121, undergoes resonance when avoltage of the predetermined frequency is applied to the piezoelectricelements 120 a and 120 b. As a result, the ratio between the bendingrigidities the X- and Y-axial parts of the vibrator 173 comes to have apredetermined value. The vibrator 173 therefore generates such a bendingvibration of large amplitude as shown in FIGS. 4A to 4C.

As shown in FIG. 3, signal electrodes 174 a and 175 a are formed on thepiezoelectric element 120 a, and signal electrodes 174 b and 175 b areformed on the piezoelectric element 120 b. Note that the hatched partsshown in FIG. 3 show the shapes of the signal electrodes clearly, not toillustrating the sections thereof. The signal electrodes 175 a and 175 bare provided on the back opposing the signal electrodes 174 a and 174 b,and are bent toward that surface of the piezoelectric element 120 a, onwhich the signal electrodes 174 a and 174 b are provided. The flex 158 ahaving the above-mentioned conductive pattern is electrically connectedto the signal electrode 174 a and signal electrode 175 a. The flex 158 bhaving the above-mentioned conductive pattern is electrically connectedto the signal electrode 174 b and signal electrode 175 b. To the signalelectrodes 174 a, 174 b, 175 a and 175 b, a drive voltage of theprescribed frequency is applied form the dust filter control circuit 122through flexes 158 a and 158 b. The drive voltage, thus applied, cancause the dust filter 119 to undergo such a two-dimensional,standing-wave bending vibration as is shown in FIGS. 4A to 4C. Thosesides of the dust filter 119, at which the piezoelectric elements 120 aand 120 b are arranged, have length LA. The piezoelectric elements 120 aand 120 b have length Dx. (This size notation accords with the sizenotation used in FIG. 5.) Since the dust filter 119 shown in FIG. 4A isrectangular, it is identical in shape to the “virtual rectangle”according to this invention (later described). Hence, the long sides LAof the dust filter 119 are identical to the sides LF of the virtualrectangle that include the sides LA.

The bending rigidity Eix of the X-axial part is expressed as:Eix=Eb×Ib+Ed×Id. Here, Ib is the second moment of area around theneutral axis of a section (i.e., section shown in FIG. 4B) whichincludes the X-axis 176 (FIG. 4A) and which is perpendicular to thesurface of the dust filter 119; Eb is the elastic modulus of the dustfilter 119; Id is the second moment of area around the neutral axis ofthe elastic members 121; and Ed is the elastic modulus of the elasticmembers 121.

The bending rigidity Eiy of the Y-axial part is expressed as:Eiy=Eb×Ib′+Es×Is. Here, Ib′ is the second moment of area around theneutral axis of a section (i.e., section shown in FIG. 4C) whichincludes the Y-axis 177 (FIG. 4A) and which is perpendicular to thesurface of the dust filter 119; Eb is the elastic modulus of the dustfilter 119; Is the second moment of area around the neutral axis of thepiezoelectric elements 120 a and 120 b; and Es is the elastic modulus ofthe piezoelectric elements 120 a and 120 b. The ratio of the length Dxof the piezoelectric elements 120 a and 120 b to the length LA the dustfilter 119 has in the lengthwise direction of the piezoelectric elements120 a and 120 b, i.e., Dx/LA, is 0.5 or more. Similarly, the ratio ofthe length Cy (in size notation of FIG. 5) of the elastic members 121 tothe length LB the dust filter 119 has in the lengthwise direction of theelastic members 121, i.e., Cy/LB, is 0.5 or more. If the bendingrigidities are represented by the above-mentioned sections, ratio Dx/LAand ration Cy/LBa will be approximately 0.5 or more because thepiezoelectric elements 120 a and 120 b and the elastic members 121 needto have a certain length each as shown in FIG. 6.

The bending vibration shown in FIG. 4A is standing wave vibration. InFIG. 4A, the blacker the streaks, each indicating a node area 178 ofvibration (i.e., area where the vibrational amplitude is small), thesmaller the vibrational amplitude is. Note that the meshes shown in FIG.4A are division meshes usually used in the final element method.

If the node areas 178 are at short intervals as shown in FIG. 4A whenthe vibration speed is high, in-plane vibration (vibration along thesurface) will occur in the node areas 178. This vibration induces alarge inertial force in the direction of the in-plane vibration (seemass point Y2 in FIG. 13, described later, which moves over the nodealong an arc around the node, between positions Y2 and Y2′) to the dustat the node areas 178. If the dust filter 119 is inclined to becomeparallel to the gravity so that a force may act along the dust receivingsurface, the inertial force and the gravity can remove the dust from thenode areas 178.

In FIG. 4A, the white areas indicate areas where the vibrationalamplitude is large. The dust adhering to any white area is removed bythe inertial force exerted by the vibration. The dust can be removedfrom the node areas 178, too, by producing vibration in another mode, atsimilar amplitude at each node area 178.

If the bending rigidity ratio Eix/Eiy, which is the ratio of the bendingrigidity of the X-axial part of the vibrator 173 to the bending rigidityof the Y-axial part thereof, is changed, the vibration speed ratio(i.e., ratio between the maximum vibration speed and each vibrationspeed) at the center (x=0, y=0) of the dust filter 119 will change asillustrated in FIG. 7. The bending moment Eix acting in the X-directionis expressed as: Eix=E·Ix/(1−ν²), where Ix is the second moment of areain the section of the vibrator, including a reinforcement member passingthe intersection of the X- and Y-axes and extending orthogonal to theX-axis, E is Young's modulus of each member, and ν is Poisson's ratio ofeach member. Further, the bending moment Eiy acting in the Y-directionis expressed as: Eiy=E·Iy/(1−ν²), where Iy is the second moment of areain the section of the vibrator, including a reinforcement member passingthe intersection of the X- and Y-axes and extending orthogonal to theY-axis, E is Young's modulus of each member, and ν is Poisson's ratio ofeach member. In FIG. 7, the square dot (▪) pertains to the vibrationalmode shown in FIG. 4A. If the vibration ratio is 1, i.e., the peak ofthe solid curve (FIG. 7), the vibrational mode is such a type as shownin FIG. 8. As seen from FIG. 7, the vibration speed ratio, i.e., theratio of the vibration speed to the maximum speed, can be 0.7 or moreand a desirable vibration speed can be attained if the bending rigidityratio Eix/Eiy of the vibrator 173 is about 0.4 or more, but less than1.0. The maximum speed ratio, i.e., 1.0, can be attained if the bendingrigidity ratio Eix/Eiy is almost 0.7.

The graph of FIG. 7 shows the case where the length ratio of eithershort side of the dust filter 119 to either long side thereof is 0.89.The left end of the solid curve pertains to the case where no elasticmembers 121 are attached, and shows that the maximum speed can beachieved by attaching the elastic members 121. The vibrational mode atthe left end of the solid curve is such a conventional vibrational modeas shown in FIG. 9. That is, even if the length ratio of either shortside of the dust filter 119 to either long side thereof does not fallwithin such a range that optimizes the vibration speed, the vibrationspeed can be increased merely by arranging the elastic members 121 arearranged on the dust filter 119 so that the bending rigidity ratiobetween the X- and Y-axes may be a predetermined value.

Synthesis of vibrational modes will be explained below. The bendingvibrational mode shown in FIG. 4A is achieved by synthesizing thebending vibration of the X-direction and the bending vibration of theY-direction. The fundamental state of this synthesis is shown in FIG.10. If the vibrator 173 is put on a member that little attenuatesvibration, such as a foamed rubber block, and then made to vibratefreely, a vibrational mode of producing such lattice-shaped node areas178 as shown in FIG. 9 will be usually attained easily (see Jpn. Pat.Appln. KOKAI Publication No. 2007-228246, identified above). In thefront view included in FIG. 10, the broken lines define the node areas178 shown in FIG. 9 (more precisely, the lines indicate the positionswhere the vibrational amplitude is minimal in the widthwise direction oflines). In this case, a standing wave, bending vibration at wavelengthλ_(x) occurs in the X-direction, and a standing wave, bending vibrationat wavelength λ_(y) occurs in the Y-direction. These standing waves aresynthesized as shown in FIG. 9. With respect to the origin (x=0, y=0),the vibration Z (x, y) at a given point P (x, y) is expressed byEquation 1, as follows:Z(x,y)=A·W _(mn)(x,y)·cos(γ)+A·W _(nm)(x,y)·sin(γ)  (1)where A is amplitude (a fixed value here, but actually changing with thevibrational mode or the power supplied to the piezoelectric elements); mand n are positive integers including 0, indicating the order of naturalvibration corresponding to the vibrational mode; γ is a given phaseangle;

${{W_{mn}\left( {x,y} \right)} = {{\sin\left( {{n\;{\pi\; \cdot x}} + \frac{\pi}{2}} \right)} \cdot {\sin\left( {{m\;{\pi \cdot y}} + \frac{\pi}{2}} \right)}}};{and}$${W_{n\; m}\left( {x,y} \right)} = {{\sin\left( {{m\;{\pi \cdot x}} + \frac{\pi}{2}} \right)} \cdot {{\sin\left( {{n\;{\pi \cdot y}} + \frac{\pi}{2}} \right)}.}}$

Assume that the phase angle γ is 0 (γ=0). Then, Equation 1 changes to:

$\begin{matrix}{{Z\left( {x,y} \right)} = {A \cdot {W_{mn}\left( {x,y} \right)}}} \\{= {A \cdot {\sin\left( {\frac{n \cdot \pi \cdot x}{\lambda_{x}} + \frac{\pi}{2}} \right)} \cdot {{\sin\left( {\frac{m \cdot \pi \cdot y}{\lambda_{y}} + \frac{\pi}{2}}\; \right)}.}}}\end{matrix}$Further assume that λ_(x)=λ_(y)=λ=1 (x and y are represented by the unitof the wavelength of bending vibration). Then:

$\begin{matrix}{{Z\left( {x,y} \right)} = {A \cdot {W_{mn}\left( {x,y} \right)}}} \\{= {A \cdot {\sin\left( {{n \cdot \pi \cdot x} + \frac{\pi}{2}} \right)} \cdot {{\sin\left( {{m \cdot \pi \cdot y} + \frac{\pi}{2}} \right)}.}}}\end{matrix}$FIG. 9 shows the vibrational mode that is applied if m=n (since theX-direction vibration and the Y-direction vibration are identical interms of order and wavelength, the dust filter 119 has a square shape).In this vibrational mode, the peaks, nodes and valleys of vibrationappear at regular intervals in both the X-direction and the Y-direction,and vibration node areas 178 appear as a checkerboard pattern(conventional vibrational mode). In the vibrational mode where m=0, n=1,the vibration has peaks, nodes and valleys parallel to a side (LB) thatextends parallel to the Y-direction. In the vibrational mode identifiedwith a checkerboard pattern or peaks, nodes and valleys parallel to aside, the X-direction vibration and the Y-direction vibration remainindependent, never synthesized to increase the vibrational amplitude.

In view of this, the dust filter 119 may be elongated a little, shapedlike a rectangle, and may be vibrated at a specific frequency, or in amode where m=3 and n=2. In this vibrational mode, the phase angle γ is+π/4 or ranges from −π/4 to −π/8. This vibrational mode is a mode inwhich the present embodiment will have very large vibrational amplitude(the maximum amplitude is at the same level as at the conventionalcircular dust filter). The phase angle γ can be changed by changing thebending rigidity ratio as in the present embodiment, achievingvibrational modes if γ=+π/4 or γ=−π/4 to −π/8. If the phase angle γ isabout +π/4, the vibrational mode will be the mode shown in FIG. 4A. Inthis vibrational mode, the peak ridges 179 of vibrational amplitude formclosed loops around the optical axis though the dust filter 119 isrectangular. Consequently, a reflected wave coming from a side extendingin the X-direction and a reflected wave coming from a side extending inthe Y-direction are efficiently combined, forming a standing wave. Ifthe phase angle γ is about −π/4, the vibrational mode of FIG. 8 will berealized. In this vibrational mode, peak ridges 179 of vibrationalamplitude are formed, surrounding the midpoint of each side. That is,the center of the dust filter 119 becomes a node area 178 wherevibrational amplitude is scarcely observed. Peak ridges 179 ofvibrational amplitude are formed, surrounding the midpoint of each side.In the vibration of FIG. 4A or FIG. 8, the vibration speed (see FIG. 7)can be increased about 50% over the vibration speed achieved in theconventional vibrational mode (see FIG. 9) wherein the nodes of bendingvibration form a lattice pattern.

The dust filter 119 of the vibrator 173, shown in FIG. 4A, is a glassplate (optical element) having a size of 30.8 mm (X-direction: LA,LF)×28.5 mm (Y-direction: LB)×0.65 mm (thickness: T). The dust filter119 is rectangular, having long sides LA (30.8 mm, extending in theX-direction) and short sides LB (34.5 mm). Therefore, the dust filter119 is identical to the “virtual rectangle” according to this invention,which has the same area as the dust filter 119. The long sides LA of thedust filter 119 are arranged are thus identical to the sides LF of thevirtual rectangle that includes the sides LA. The piezoelectric elements120 a and 120 b are made of lead titanate-zirconate ceramic and have asize of 21 mm (X-direction: Dx)×3 mm (Y-direction: Dy)×0.8 mm(thickness: Dz). The piezoelectric elements 120 a and 120 b are adheredwith epoxy-based adhesive to the dust filter 119, extending along theupper and lower sides of the filter 119 (optical element), respectively.More specifically, the piezoelectric elements 120 a and 120 b extend inthe X-direction and arranged symmetric in the left-right direction, withrespect to the centerline (the Y-axis 177) of the dust filter 119, whichextends in the Y-direction. The elastic members 121 are made of the samematerial as the dust filter 119. That is, they are glass plates, eachhaving a size of 1 mm (X-direction: Cx)×26 mm (Y-direction: Cy)×1 mm(thickness: Cz). The elastic members 121 are arranged symmetric withrespect to the X-axis 176 and the Y-axis 177, and are spaced by distanceD in the X-direction, where D=24.8 mm. In this case, the resonancefrequency in the vibrational mode of FIG. 4A is in the vicinity of 80kHz.

The dust filter 119 of the vibrator 173, shown in FIG. 8, is a glassplate (optical element) having a size of 30.8 mm (X-direction: LA,LF)×34.5 mm (Y-direction: LB)×0.65 mm (thickness: T). The dust filter119 is rectangular, having long sides LA (30.8 mm, extending in theX-direction) and short sides LB (34.5 mm). Therefore, the dust filter119 is identical to the “virtual rectangle” according to this invention,which has the same area as the dust filter 119. The long sides LA of thedust filter 119 are arranged are thus identical to the sides LF of thevirtual rectangle that includes the sides LA. The piezoelectric elements120 a and 120 b are made of lead titanate-zirconate ceramic and have asize of 21 mm (X-direction: Dx)×3 mm (Y-direction: Dy)×0.8 mm(thickness: Dz). The piezoelectric elements 120 a and 120 b are adheredwith epoxy-based adhesive to the dust filter 119, extending along theupper and lower sides of the filter 119 (optical element), respectively.More specifically, the piezoelectric elements 120 a and 120 b extend inthe X-direction and arranged symmetric in the left-right direction, withrespect to the centerline (the Y-axis 177) of the dust filter 119, whichextends in the Y-direction. The elastic members 121 are made of the samematerial as the dust filter 119. That is, they are glass plates, eachhaving a size of 1 mm (X-direction: Cx)×26 mm (Y-direction: Cy)×1 mm(thickness: Cz). The elastic members 121 are arranged symmetric withrespect to the X-axis 176 and the Y-axis 177, and are spaced by distanceD in the X-direction, where D=28.8 mm. In this case, the resonancefrequency in the vibrational mode of FIG. 8 is in the vicinity of 92kHz. That is, the vibrational mode can be changed from the mode of FIG.4A to the mode of FIG. 8 if the elastic members 121 are adjusted inposition and the phase angle γ is thereby changed. In the vibrationalmode of FIG. 8, peak ridges 179 of vibrational amplitude are formed,surrounding the midpoints of the sides that are parallel to the Y-axis177. In this case, the phase angle γ of bending vibration is about −π/4,at which the vibration speed is high.

FIG. 11 shows a modification of the vibrator 173. The modified vibrator173 has a dust filter 119 that is D-shaped, formed by cutting a part ofa plate shaped like a disc, thus defining one side. That is, themodified vibrator 173 uses a D-shaped dust filter 119 that has a sidesymmetric with respect to the symmetry axis (the Y-axis 177) extendingin the Y-direction. The piezoelectric element 120 a is arranged on thesurface of the dust filter 119, extending parallel to that side andpositioned symmetric with respect to the midpoint of the side (or to asymmetry axis (the Y-axis 177) extending in the Y-direction). On theother hand, the piezoelectric element 120 b is substantially inscribedin the outer circumference of the dust filter 119 and extends parallelto that side of the dust filter 119. The elastic members 121, which areshaped like an arc, are arranged symmetric with respect to the Y-axis177, each extending along the circumference of the dust filter 119. Soshaped, the dust filter 119 is more symmetric with respect to its center(regarded as the centroid), and can more readily vibrate in a statedesirable to the present embodiment. In addition, the dust filter 119can be smaller than the circular one. Furthermore, since thepiezoelectric elements 120 a and 120 b are arranged, each parallel tothose sides of the dust filter 119, which have notches, the asymmetry interms vibration, resulting from the cutting, can be made more symmetricby increasing the rigidity. This helps to render the vibration statemore desirable. Further, this increases the area in which the elasticmembers 121 are arranged to adjust the rigidity. The rigidity cantherefore be adjusted more than otherwise. Note that the long side andshort side shown in FIG. 11 are the long and short sides of a virtualrectangle 180 which has the same area as the dust filter 119, one sideof which includes the above-mentioned one side of the dust filter 119,and the opposite side of which extends along an outer side of thepiezoelectric element 120 b.

FIG. 12 shows another modification of the vibrator 173. This modifiedvibrator 173 has a dust filter 119 is formed by cutting a circular platealong two parallel lines, forming two parallel sides. That is, themodified vibrator 173 uses a dust filter 119 that has two sidessymmetric with respect to the symmetry axis (the Y-axis 177) extendingin the Y-direction. In this case, actuate piezoelectric elements 120 aand 120 b are arranged not on the straight sides, but on the curvedparts defining a circle. The elastic members 121 for adjusting therigidity are arranged symmetry with respect to the X-axis 176 and theY-axis 177, extending along the symmetric sides. Since the dust filter119 is so shaped, the piezoelectric elements 120 a and 120 b arearranged, efficiently providing a smaller vibrator 173. Note that thelong side and shot side shown in FIG. 12 are the long and short sides ofa virtual rectangle 180 which has the same area as the dust filter 119,two opposite sides of which extend along the opposite two sides of thedust filter 119, respectively. The piezoelectric elements 120 a and 120b are arranged at the short sides. The piezoelectric elements 120 a and120 b have length Dx as measured along the short sides (having lengthLB) of the virtual rectangle 177.

A method of removing dust will be explained in detail, with reference toFIG. 13. FIG. 13 shows a cross section identical to that shown in FIG.4B. Assume that the piezoelectric elements 120 a and 120 b are polarizedin the direction of arrow 181 as shown in FIG. 13. If a voltage of aspecific frequency is applied to the piezoelectric elements 120 a and120 b at a certain time t₀, the vibrator 173 will be deformed asindicated by solid lines. At the mass point Y existing at given positiony in the surface of the vibrator 173, the vibration z in the Z-directionis expressed by Equation 2, as follows:z=A·sin(Y)·cos(ωt)  (2)where ω is the angular velocity of vibration, A is the amplitude ofvibration in the Z-direction, and Y=2 πy/λ (λ: wavelength of bendingvibration).

The Equation 2 represents the standing-wave vibration shown in FIG. 4A.Thus, if y=s·λ/2 (here, is an integer), then Y=sπ, and sin(Y)=0. Hence,a node 182, at which the amplitude of vibration in the Z-direction iszero irrespective of time, exists for every π/2. This is standing-wavevibration. The state indicated by broken lines in FIG. 13 takes place ift=kπ/ω (k is odd), where the vibration assumes a phase opposite to thephase at time t₀.

Vibration z(Y₁) at point Y₁ on the dust filter 119 is located at anantinode 183 of standing wave, bending vibration. Hence, the vibrationin the Z-direction has amplitude A, as expressed in Equation 3, asfollows:z(Y ₁)=A·cos(ωt)  (3)

If Equation 3 is differentiated with time, the vibration speed Vz(Y₁) atpoint Y₁ is expressed by Equation 4, below, because ω=2πf, where f isthe frequency of vibration:

$\begin{matrix}{{{Vz}\left( Y_{1} \right)} = {\frac{\mathbb{d}\left( {z\left( Y_{1} \right)} \right)}{\mathbb{d}t} = {{- 2}\;\pi\;{f \cdot A \cdot {\sin\left( {\omega\; t} \right)}}}}} & (4)\end{matrix}$If Equation 4 is differentiated with time, vibration acceleration αz(Y₁)is expressed by Equation 5, as follows:

$\begin{matrix}{{\alpha\;{z\left( Y_{1} \right)}} = {\frac{\mathbb{d}\left( {{Vz}\left( Y_{1} \right)} \right)}{\mathbb{d}t} = {{- 4}\pi^{2}{f^{2} \cdot A \cdot {\cos\left( {\omega\; t} \right)}}}}} & (5)\end{matrix}$Therefore, the dust 184 adhering at point Y₁ receives the accelerationof Equation 5. The inertial force Fk the dust 184 receives at this timeis given by Equation 6, as follows:Fk=αz(Y ₁)·M=−4π² f ² ·A·cos(ωt)·M  (6)where M is the mass of the dust 184.

As can be seen from Equation 6, the inertial force Fk increases asfrequency f is raised, in proportion to the square of f. However, theinertial force cannot be increased if amplitude A is small, no matterhow much frequency f is raised. Generally, kinetic energy of vibrationcan be produced, but in a limited value, if the piezoelectric elements120 a and 120 b that produce the kinetic energy have the same size.Therefore, if the frequency is raise in the same vibrational mode,vibrational amplitude A will change in inverse proportion to the squareof frequency f. Even if the resonance frequency is raised to achieve ahigher-order resonance mode, the vibrational frequency will fall, notincreasing the vibration speed or the vibration acceleration. Rather, ifthe frequency is raised, ideal resonance will hardly be accomplished,and the loss of vibrational energy will increase, inevitably decreasingthe vibration acceleration. That is, the mode cannot attain largeamplitude if the vibration is produced in a resonance mode that useshigh frequency only. The dust removal efficiency will be much impaired.

Although the dust filter 119 is rectangular, the peak ridges 179 ofvibrational amplitude form closed loops around the optical axis in thevibrational mode of the embodiment, which is shown in FIG. 4A. In thevibrational mode of the embodiment, which is shown in FIG. 8, the peakridges 179 of vibrational amplitude form curves surrounding the midpointof each side. The wave reflected from the side extending in theX-direction and the wave reflected from the side extending in theY-direction are efficiently synthesized, forming a standing wave.

The vibration speed at the center position of the dust filter 119, asmeasured in the Z-direction, provides the widest possible region whenthe length ratio Dx/LA of the piezoelectric elements is set at a valueless than 1 (i.e., by making the length LP of the piezoelectric elements120 a and 120 b equal to that of the sides of the dust filter 119), notat 1. This is obvious from FIG. 6, in which the length ratio Dx/LA ofthe piezoelectric elements 120 a and 120 b is plotted against theabscissa (LA (or LF): the length of the dust filter 119 (or that of thevirtual rectangle) having a side on which the piezoelectric elements 120a and 120 b are arranged; Dx: the length of the piezoelectric elements120 a and 120 b arranged in parallel to length LA), and the vibrationspeed ratio at the center of the filter is plotted against the ordinate.In FIG. 6, the ratio (V/V_(max)) of the vibration speed V to the maximumvibration speed V_(max) possible in this region is plotted on theordinate. The maximum value of the length ratio of the piezoelectricelements is, of course, 1. If the length ratio of the piezoelectricelements is 0.5 or less, the vibration speed ratio will be less than0.8. This means that the speed is lower than the maximum value by 20% ormore. Hence, it is preferable for the length ratio of the piezoelectricelements to be 0.5 or more, but less than 1, in order to increase thevibration speed at the center of the dust filter 119, with respect tothe Z-direction (to 0.7 or more).

On the circular dust filter, all lines extending from its circumferenceto its center have the same length. Hence, the waves reflected from thecircumference can be synthesized at the highest efficiency. Thevibrational amplitude, which is perpendicular to the surface of thecircular dust filter, can be extremely large. The vibrational amplitudeis actually very large. In vibration wherein the peak ridges 179 ofvibrational amplitude form closed loops around the optical axis or thepeak ridges 179 form curves surrounding the midpoint of each sideaccording to this embodiment, the dust filter 119 can undergo vibrationof amplitude a similar to that of concentric vibration that may occur ifthe dust filter 119 has a disc shape. In any vibrational mode in whichthe amplitude is simply parallel to the side (see FIG. 9), the vibrationacceleration is only 10% or more of the acceleration achieved in thisembodiment.

In the vibration wherein the peak ridges 179 of vibrational amplitudeform closed loops or curves surrounding the midpoint of each side, thevibrational amplitude is the largest at the center of the vibrator 173and small at the closed loop or the curve at circumferential edges.Thus, the dust removal capability is maximal at the center of the image.If the center of the vibrator 173 is aligned with the optical axis, theshadow of dust 184 will not appear in the center part of the image,which has high image quality. This is an advantage.

In the vibration node areas 178, which exist in the focusing-beampassing area, the nodes 182 may be changed in position by changing thedrive frequencies of the piezoelectric elements 120 a and 120 b. Then,the elements 120 a and 120 b resonate in a different vibrational mode,whereby the dust can be removed, of course.

A vibration state that is attained if the piezoelectric elements 120 aand 120 b are driven at a frequency near the resonance frequency will bedescribed with reference to FIGS. 14A and 14B. FIG. 14A shows anequivalent circuit that drives the piezoelectric elements 120 a and 120b at a frequency near the resonance frequency. In FIG. 14A, C₀ is theelectrostatic capacitance attained as long as the piezoelectric elements120 a and 120 b remain connected in parallel, and L, C and R are thevalues of a coil, capacitor and resistor that constitute an electriccircuit equivalent to the mechanical vibration of the vibrator 173.Naturally, these values change with the frequency.

When the frequency changes to resonance frequency f₀, L and C achieveresonance as is illustrated in FIG. 14B. As the frequency is graduallyraised toward the resonance frequency from the value at which noresonance takes place, the vibration phase of the vibrator 173 changeswith respect to the phase of vibration of the piezoelectric elements 120a and 120 b. When the resonance starts, the phase reaches π/2. As thefrequency is further raised, the phase reaches n. If the frequency israised even further, the phase starts decreasing. When the frequencycomes out of the resonance region, the phase becomes equal to the phasewhere no resonance undergoes at low frequencies. In the actualsituation, however, the vibration state does not become ideal. The phasedoes not change to π in some cases. Nonetheless, the drive frequency canbe set to the resonance frequency.

Support areas 185 existing at the four corners, as shown in FIGS. 4A and8, are areas in which virtually no vibration takes place. Therefore,these parts are pushed in the Z-direction, holding the dust filter 119through the cushion members 153 and 154 made of vibration-attenuatingmaterial such as rubber. So held, the dust filter 119 can be reliablysupported without attenuating the vibration. In other words, the cushionmembers 153 and 154 made of rubber or the like scarcely attenuate thein-plane vibration, because they allow the dust filter 119 to vibrate inplane.

On the other hand, the seal 157 must be provided in the area havingvibrational amplitude, too. In the vibrational mode of the presentinvention, the peripheral vibrational amplitude is small. In view ofthis, the dust filter 119 is supported, at circumferential edge, by thelip-shaped part of the seal 157, thereby applying no large force in thedirection of bending vibrational amplitude. Therefore, the seal 157attenuates, but very little, the vibration whose amplitude is inherentlysmall. As shown in FIGS. 4A and 8, as many seal-contact parts 186 aspossible contact the node areas 178 in which the vibrational amplitudeis small. This further reduces the attenuation of vibration.

The prescribed frequency at which to vibrate the piezoelectric elements120 a and 120 b is determined by the shape, dimensions, material andsupported state of the dust filter 119, which is one component of thevibrator 173. In most cases, the temperature influences the elasticitycoefficient of the vibrator 173 and is one of the factors that changethe natural frequency of the vibrator 173. Therefore, it is desirable tomeasure the temperature of the vibrator 173 and to consider the changein the natural frequency of the vibrator 173, before the vibrator 173 isused. A temperature sensor (not shown) is therefore connected to atemperature measuring circuit (not shown), in the digital camera 10. Thevalue by which to correct the vibrational frequency of the vibrator 173in accordance with the temperature detected by the temperature sensor isstored in the nonvolatile memory 129. Then, the measured temperature andthe correction value are read into the Bucom 101. The Bucom 101calculates a drive frequency, which is used as drive frequency of thedust filter control circuit 122. Thus, vibration can be produced, whichis efficient with respect to temperature changes, as well.

The dust filter control circuit 122 of the digital camera 10 accordingto this invention will be described below, with reference to FIGS. 15and 16. The dust filter control circuit 122 has such a configuration asshown in FIG. 15. The components of the dust filter control circuit 122produce signals (Sig1 to Sig4) of such waveforms as shown in the timingchart of FIG. 16. These signals will control the dust filter 119, aswill be described below.

More specifically, as shown in FIG. 15, the dust filter control circuit122 comprises a N-scale counter 187, a half-frequency dividing circuit188, an inverter 190, a plurality of MOS transistors Q₀₀, Q₀₁ and Q₀₂, atransformer 191, and a resistor R₀₀.

The dust filter control circuit 122 is so configured that a signal(Sig4) of the prescribed frequency is produced at the secondary windingof the transformer 191 when MOS transistors Q₀₁ and Q₀₂ connected to theprimary winding of the transformer 191 are turned on and off. The signalof the prescribed frequency drives the piezoelectric elements 120 a and120 b, thereby causing the vibrator 173, to which the dust filter 119 issecured, to produce a resonance standing wave.

The Bucom 101 has two output ports P_PwCont and D_NCnt provided ascontrol ports, and a clock generator 192. The output ports P_PwCont andD_NCnt and the clock generator 192 cooperate to control the dust filtercontrol circuit 122 as follows. The clock generator 192 outputs a pulsesignal (basic clock signal) having a frequency much higher than thefrequency of the signal that will be supplied to the piezoelectricelements 120 a and 120 b. This output signal is signal Sig1 that has thewaveform shown in the timing chart of FIG. 16. The basic clock signal isinput to the N-scale counter 187.

The N-scale counter 187 counts the pulses of the pulse signal. Everytime the count reaches a prescribed value “N,” the N-scale counter 187produces a count-end pulse signal. Thus, the basic clock signal isfrequency-divided by N. The signal the N-scale counter 187 outputs issignal Sig2 that has the waveform shown in the timing chart of FIG. 16.

The pulse signal produced by means of frequency division does not have aduty ratio of 1:1. The pulse signal is supplied to the half-frequencydividing circuit 188. The half-frequency dividing circuit 188 changesthe duty ratio of the pulse signal to 1:1. The pulse signal, thuschanged in terms of duty ratio, corresponds to signal Sig3 that has thewaveform shown in the timing chart of FIG. 16.

While the pulse signal, thus changed in duty ratio, is high, MOStransistor Q₀₁ to which this signal has been input is turned on. In themeantime, the pulse signal is supplied via the inverter 190 to MOStransistor Q₀₂. Therefore, while the pulse signal (signal Sig3) is lowstate, MOS transistor Q₀₂ to which this signal has been input is turnedon. Thus, the transistors Q₀₁ and Q₀₂, both connected to the primarywinding of the transformer 191, are alternately turned on. As a result,a signal Sig4 of such frequency as shown in FIG. 16 is produced in thesecondary winding of the transformer 191.

The winding ratio of the transformer 191 is determined by the outputvoltage of the power-supply circuit 136 and the voltage needed to drivethe piezoelectric elements 120 a and 120 b. Note that the resistor R₀₀is provided to prevent an excessive current from flowing in thetransformer 191.

In order to drive the piezoelectric elements 120 a and 120 b, MOStransistor Q₀₀ must be on, and a voltage must be applied from thepower-supply circuit 136 to the center tap of the transformer 191. Inthis case, MOS transistor Q₀₀ is turned on or off via the output portP_PwCont of the Bucom 101. Value “N” can be set to the N-scale counter187 from the output port D_NCnt of the Bucom 101. Thus, the Bucom 101can change the drive frequency for the piezoelectric elements 120 a and120 b, by appropriately controlling value “N.”

The frequency can be calculated by using Equation 7, as follows:

$\begin{matrix}{{fdrv} = \frac{fpls}{2N}} & (7)\end{matrix}$where N is the value set to the N-scale counter 187, fpls is thefrequency of the pulse output from the clock generator 192, and fdrv isthe frequency of the signal supplied to the piezoelectric elements 120 aand 120 b.

The calculation based on Equation 7 is performed by the CPU (controlunit) of the Bucom 101.

If the dust filter 119 is vibrated at a frequency in the ultrasonicregion (i.e., 20 kHz or more), the operating state of the dust filter119 cannot be aurally discriminated, because most people cannot hearsound falling outside the range of about 20 to 20,000 Hz. This is whythe operation display LCD 130 or the operation display LED 131 has adisplay unit for showing how the dust filter 119 is operating, to theoperator of the digital camera 10. More precisely, in the digital camera10, the vibrating members (piezoelectric elements 120 a and 120 b)imparts vibration to the dust-screening member (dust filter 119) that isarranged in front of the CCD 117, can be vibrated and can transmitlight. In the digital camera 10, the display unit is operated ininterlock with the vibrating member drive circuit (i.e., dust filtercontrol circuit 122), thus informing how the dust filter 119 isoperating (later described in detail).

To explain the above-described characteristics in detail, the controlthe Bucom 101 performs will be described with reference to FIGS. 17A to21. FIGS. 17A and 17B show the flowchart that relates to the controlprogram, which the Bucom 101 starts executing when the power switch (notshown) provided on the body unit 100 of the camera 10 is turned on.

First, a process is performed to activate the digital camera 10 (StepS101). That is, the Bucom 101 control the power-supply circuit 136. Socontrolled, the power-supply circuit 136 supplies power to the othercircuit units of the digital camera 10. Further, the Bucom 101initializes the circuit components.

Next, the Bucom 101 calls a sub-routine “silent vibration,” vibratingthe dust filter 119, making no sound (that is, at a frequency fallingoutside the audible range) (Step S102). The “audible range” ranges fromabout 200 to 20,000 Hz, because most people can hear sound fallingwithin this range.

Steps S103 to S124, which follow, make a group of steps that iscyclically repeated. That is, the Bucom 101 first detects whether anaccessory has been attached to, or detached from, the digital camera 10(Step S103). Whether the lens unit 200 (i.e., one of accessories), forexample, has been attached to the body unit 100 is detected. Thisdetection, e.g., attaching or detaching of the lens unit 200, isperformed as the Bucom 101 communicates with the Lucom 201.

If a specific accessory is detected to have been attached to the bodyunit 100 (YES in Step S104), the Bucom 101 calls a subroutine “silentvibration” and causes the dust filter 119 to vibrate silently (StepS105).

While an accessory, particularly the lens unit 200, remains not attachedto the body unit 100 that is the camera body, dust is likely to adhereto each lens, the dust filter 119, and the like. It is thereforedesirable to perform an operation of removing dust at the time when itis detected that the lens unit 200 is attached to the body unit 100. Itis highly possible that dust adheres as the outer air circulates in thebody unit 100 at the time a lens is exchanged with another. It istherefore advisable to remove dust when a lens is exchange with another.Then, it is determined that photography will be immediately performed,and the operation goes to Step S106.

If a specific accessory is not detected to have been attached to thebody unit 100 (NO in Step S104), the Bucom 101 goes to the next step,i.e., Step S106.

In Step S106, the Bucom 101 detects the state of a specific operationswitch that the digital camera 10 has.

That is, the Bucom 101 determines whether the first release switch (notshown), which is a release switch, has been operated from the on/offstate of the switch (Step S107). The Bucom 101 reads the state. If thefirst release switch has not been turned on for a predetermined time,the Bucom 101 discriminates the state of the power switch (Step S108).If the power switch is on, the Bucom 101 returns to Step S103. If thepower switch is off, the Bucom 101 performs an end-operation (e.g.,sleep).

On the other hand, the first release switch may be found to have beenturned on in Step S107. In this case, the Bucom 101 acquires theluminance data about the object, from the photometry circuit 115, andcalculates from this data an exposure time (Tv value) and a diaphragmvalue (Av value) that are optimal for the image acquisition unit 116 andlens unit 200, respectively (Step S109).

Thereafter, the Bucom 101 acquires the detection data from the AF sensorunit 109 through the AF sensor drive circuit 110, and calculates adefocus value from the detection data (Step S110). The Bucom 101 thendetermines whether the defocus value, thus calculated, falls within apreset tolerance range (Step S111). If the defocus value does not fallwithin the tolerance range, the Bucom 101 drives the photographic lens202 (Step S112) and returns to Step S103.

On the other hand, the defocus value may falls within the tolerancerange. In this case, the Bucom 101 calls the subroutine “silentvibration” and causes the dust filter 119 to vibrate silently (StepS113).

Further, the Bucom 101 determines whether the second release switch (notshown), which is another release switch, has been operated (Step S114).If the second release switch is on, the Bucom 101 goes to Step S115 andstarts the prescribed photographic operation (later described indetail). If the second release switch is off, the Bucom 101 returns toStep S108.

During the image acquisition operation, the electronic image acquisitionis controlled for a time that corresponds to the preset time forexposure (i.e., exposure time), as in ordinary photography.

As the above-mentioned photographic operation, Steps S115 to S121 areperformed in a prescribed order to photograph an object. First, theBucom 101 transmits the Av value to the Lucom 201, instructing the Lucom201 to drive the diaphragm 203 (Step S115). Thereafter, the Bucom 101moves the quick return mirror 105 to the up position (Step S116). Then,the Bucom 101 causes the front curtain of the shutter 108 to startrunning, performing open control (Step S117). Further, the Bucom 101makes the image process controller 127 perform “image acquisitionoperation” (Step S118). When the exposure to the CCD 117 (i.e.,photography) for the time corresponding to the Tv value ends, the Bucom101 causes the rear curtain of the shutter 108 to start running,achieving CLOSE control (Step S119). Then, the Bucom 101 drives thequick return mirror 105 to the down position and cocks the shutter 108(Step S120).

Then, the Bucom 101 instructs the Lucom 210 to move the diaphragm 203back to the open position (Step S121). Thus, a sequence of imageacquisition steps is terminated.

Next, the Bucom 101 determines whether the recording medium 128 isattached to the body unit 100 (Step S122). If the recording medium 128is not attached, the Bucom 101 displays an alarm (Step S123). The Bucom101 then returns to Step S103 and repeats a similar sequence of steps.

If the recording medium 128 is attached, the Bucom 101 instructs theimage process controller 127 to record the image data acquired byphotography, in the recording medium 128 (Step S124). When the imagedata is completely recorded, the Bucom 101 returns to Step S103 againand repeats a similar sequence of steps.

In regard to the detailed relation between the vibration state and thedisplaying state will be explained in detail, the sequence ofcontrolling the “silent vibration” subroutine will be explained withreference to FIGS. 18 to 21. The term “vibration state” means the stateof the vibration induced by the piezoelectric elements 120 a and 120 b,i.e., vibrating members. FIG. 22 shows the form of a resonance-frequencywave that is continuously supplied to the vibrating members duringsilent vibration. The subroutine of FIG. 18, i.e., “silent vibration,”and the subroutine of FIGS. 19 to 21, i.e., “display process” areroutines for accomplishing vibration exclusively for removing dust fromthe dust filter 119. Vibrational frequency f₀ is set to a value close tothe resonance frequency of the dust filter 119. In the vibrational modeof FIG. 4A, for example, the vibrational frequency is 80 kHz, higherthan at least 20 kHz, and produces sound not audible to the user.

As shown in FIG. 18, when the “silent vibration” is called, the Bucom101 first reads the data representing the drive time (Toscf0) and drivefrequency (resonance frequency: Noscf0) from the data stored in aspecific area of the nonvolatile memory 129 (Step S201). At this timing,the Bucom 101 causes the display unit provided in the operation displayLCD 130 or operation display LED 131 to turn on the vibrational modedisplay, as shown in FIG. 19 (Step S301). The Bucom 101 then determineswhether a predetermined time has passed (Step S302). If thepredetermined time has not passed, the Bucom 101 makes the display unitkeep turning on the vibrational mode display. Upon lapse of thepredetermined time, the Bucom 101 turns off the displaying of thevibrational mode display (Step S303).

Next, the Bucom 101 outputs the drive frequency Noscf0 from the outputport D_NCnt to the N-scale counter 187 of the dust filter controlcircuit 122 (Step S202).

In the following steps S203 to S205, the dust is removed as will bedescribed below. First, the Bucom 101 sets the output port P_PwCont toHigh, thereby starting the dust removal (Step S203). At this timing, theBucom 101 starts displaying the vibrating operation as shown in FIG. 20(Step S311). The Bucom 101 then determines whether or not thepredetermined time has passed (Step S312). If the predetermined time hasnot passed, the Bucom 101 keeps displaying the vibrating operation. Uponlapse of the predetermined time, the Bucom 101 stops displaying of thevibrating operation (Step S313). The display of the vibrating operation,at this time, changes as the time passes or as the dust is removed (howit changes is not shown, though). The predetermined time is almost equalto Toscf0, i.e., the time for which the vibration (later described)continues.

If the output port P_PwCont is set to High in Step S203, thepiezoelectric elements 120 a and 120 b vibrate the dust filter 119 atthe prescribed vibrational frequency (Noscf0), removing the dust 184from the surface of the dust filter 119. At the same time the dust isremoved from the surface of the dust filter 119, air is vibrated,producing an ultrasonic wave. The vibration at the drive frequencyNoscf0, however, does not make sound audible to most people. Hence, theuser hears nothing. The Bucom 101 waits for the predetermined timeToscf0, while the dust filter 119 remains vibrated (Step S204). Uponlapse of the predetermined time Toscf0, the Bucom 101 sets the outputport P_PwCont to Low, stopping the dust removal operation (Step S205).At this timing, the Bucom 101 turns on the display unit, whereby thedisplaying of the vibration-end display is turned on (Step S321). Whenthe Bucom 101 determines (in Step S322) that the predetermined time haspassed, the displaying of the vibration-end display is turned off (StepS323). The Bucom 101 then returns to the step next to the step in whichthe “silent vibration” is called.

The vibrational frequency f₀ (i.e., resonance frequency Noscf0) and thedrive time (Toscf0) used in this subroutine define such a waveform asshown in the graph of FIG. 22. As can be seen from this waveform,constant vibration (f₀=80 kHz) continues for a time (i.e., Toscf0) thatis long enough to accomplish the dust removal.

That is, the vibrational mode adjusts the resonance frequency applied tothe vibrating member, controlling the dust removal.

Second Embodiment

The subroutine “silent vibration” called in the camera sequence (mainroutine) that the Bucom performs in a digital camera that is a secondembodiment of the image equipment according to this invention will bedescribed with reference to FIG. 23. FIG. 23 illustrates a modificationof the subroutine “silent vibration” shown in FIG. 18. The secondembodiment differs from the first embodiment in the operating mode ofthe dust filter 119. In the first embodiment, the dust filter 119 isdriven at a fixed frequency, i.e., frequency f₀, producing a standingwave. By contrast, in the second embodiment, the drive frequency isgradually changed, thereby achieving large-amplitude vibration atvarious frequencies including the resonance frequency, without strictlycontrolling the drive frequency.

The resonance frequency will change and the vibration speed ratio willdecrease as shown in FIG. 6 if the length ratio of the piezoelectricelements changes from the design value during the manufacture.Therefore, a precise resonance frequency must be set in each product andthe piezoelectric elements 120 a and 120 b must be driven at thefrequency so set. An extremely simple circuit configuration can,nonetheless, drive the piezoelectric elements precisely at the resonancefrequency if the frequency is controlled as in the second embodiment. Amethod of control can therefore be achieved to eliminate any differencein resonance frequency between the products.

In the subroutine “silent vibration” of FIG. 23, the vibrationalfrequency f₀ is set to a value close to the resonance frequency of thedust filter 119. The vibrational frequency f₀ is 80 kHz in, for example,the vibrational mode of FIG. 4A. That is, the vibrational frequencyexceeds at least 20 kHz, and makes sound not audible to the user.

First, the Bucom 101 reads the data representing the drive time(Toscf0), drive-start frequency (Noscfs), frequency change value (Δf)and drive-end frequency (Noscft), from the data stored in a specificarea of the nonvolatile memory 129 (Step S211). At this timing, theBucom 101 causes the display unit to display the vibrational mode asshown in FIG. 19, in the same way as in the first embodiment.

Next, the Bucom 101 sets the drive-start frequency (Noscfs) as drivefrequency (Noscf) (Step S212). The Bucom 101 then outputs the drivefrequency (Noscf) from the output port D_NCnt to the N-scale counter 187of the dust filter control circuit 122 (Step S213).

In the following steps S203 et seq., the dust is removed as will bedescribed below. First, the dust removal is started. At this time, thedisplay of the vibrating operation is performed as shown in FIG. 20, asin the first embodiment.

First, the Bucom 101 sets the output port P_PwCont to High, to achievedust removal (Step S203). The piezoelectric elements 120 a and 120 bvibrate the dust filter 119 at the prescribed vibrational frequency(Noscf), producing a standing wave of a small amplitude at the dustfilter 119. The dust cannot be removed from the surface of the dustfilter 119, because the vibrational amplitude is small. This vibrationcontinues for the drive time (Toscf0) (Step S204). Upon lapse of thisdrive time (Toscf0), the Bucom 101 determines whether the drivefrequency (Noscf) is equal to the drive-end frequency (Noscft) (StepS214). If the drive frequency is not equal to the drive-end frequency(NO in Step S214), the Bucom 101 adds the frequency change value (Δf) tothe drive frequency (Noscf), and sets the sum to the drive frequency(Noscf) (Step S215). Then, the Bucom 101 repeats the sequence of StepsS212 to S214.

If the drive frequency (Noscf) is equal to the drive-end frequency(Noscft) (YES in Step S214), the Bucom 101 sets the output port P_PwContto Low, stopping the vibration of the piezoelectric elements 120 a and120 b (Step S205), thereby terminating the “silent vibration.” At thispoint, the display of vibration-end is performed as shown in FIG. 21, asin the first embodiment.

As the frequency is gradually changed as described above, the amplitudeof the standing wave increases. In view of this, the drive-startfrequency (Ncoscfs), the frequency change value (Δf) and the drive-endfrequency (Noscft) are set so that the resonance frequency of thestanding wave may be surpassed. As a result, a standing wave of smallvibrational amplitude is produced at the dust filter 119. The standingwave can thereby controlled, such that its vibrational amplitudegradually increases until it becomes resonance vibration, and thendecreases thereafter. If the vibrational amplitude (corresponding tovibration speed) is larger than a prescribed value, the dust 184 can beremoved. In other words, the dust 184 can be removed while thevibrational frequency remains in a prescribed range. This range is broadin the present embodiment, because the vibrational amplitude is largeduring the resonance.

If the difference between the drive-start frequency (Noscfs) and thedrive-end frequency (Noscft) is large, the fluctuation of the resonancefrequency, due to the temperature of the vibrator 173 or to thedeviation in characteristic change of the vibrator 173, during themanufacture, can be absorbed. Hence, the dust 184 can be reliablyremoved from the dust filter 119, by using an extremely simple circuitconfiguration.

The present invention has been explained, describing some embodiments.Nonetheless, this invention is not limited to the embodiments describedabove. Various changes and modifications can, of course, be made withinthe scope and spirit of the invention.

For example, a mechanism that applies an air flow or a mechanism thathas a wipe may be used in combination with the dust removal mechanismhaving the vibrating member, in order to remove the dust 184 from thedust filter 119.

In the embodiments described above, the vibrating members arepiezoelectric elements. The piezoelectric elements may be replaced byelectrostrictive members or super nagnetostrictive elements. In theembodiments, two piezoelectric elements 120 a and 120 b are secured tothe dust filter 119 that is dust-screening member. Instead, only onepiezoelectric element may be secured to the dust filter 119. In thiscase, that side of the dust filter 119, to which the piezoelectricelement is secured, differs in rigidity from the other side of the dustfilter 119. Consequently, the node areas 178 where vibrational amplitudeis small will form a pattern similar to that of FIGS. 4A and 8, but willbe dislocated. Thus, it is desirable to arrange two piezoelectricelements symmetrical to each other, because the vibration can beproduced more efficiently and the dust filter 119 can be more easilyheld at four corners.

In order to remove dust more efficiently from the member vibrated, themember may be coated with an indium-tin oxide (ITO) film, which is atransparent conductive film, indium-zinc film, poly 3,4-ethylenedioxythiophene film, surfactant agent film that is a hygroscopicanti-electrostatic film, siloxane-based film, or the like. In this case,the frequency, the drive time, etc., all related to the vibration, andthe positions of the elastic members 121, are set to values that accordwith the material of the film.

Moreover, the optical LPF 118, described as one embodiment of theinvention, may be replaced by a plurality of optical LPFs that exhibitbirefringence. Of these optical LPFs, the optical LPF located closest tothe object of photography may be used as a dust-screening member (i.e.,a subject to be vibrated), in place of the dust filter 119 shown in FIG.2A.

Further, a camera may does not have the optical LPF 118 of FIG. 2Adescribed as one embodiment of the invention, and the dust filter 119may be used as an optical element such as an optical LPF, aninfrared-beam filter, a deflection filter, or a half mirror.

Furthermore, the camera may not have the optical LPF 118, and the dustfilter 119 may be replaced by the protection glass plate 143 shown inFIG. 2A. In this case, the protection glass plate 143 and the CCD chip137 remain free of dust and moisture, and the structure of FIG. 2A thatsupports and yet vibrates the dust filter 119 may be used to support andvibrate the protection glass plate 143. Needless to say, the protectionglass plate 143 may be used as an optical element such as an opticalLPF, an infrared-beam filter, a deflection filter, or a half mirror.

The embodiment described above uses elastic members 121. Nonetheless,the elastic members 121 need not be used if the dust-screening memberand/or the vibrating members are designed or arranged so that thevibrator 173 may have bending rigidity ratio Eix/Eiy of about 0.4 ormore, but less than 1.

The image equipment according to this invention is not limited to theimage acquisition apparatus (digital camera) exemplified above. Thisinvention can be applied to any other apparatus that needs a dustremoval function. The invention can be practiced in the form of variousmodifications, if necessary. More specifically, a dust moving mechanismaccording to this invention may be arranged between the display elementand the light source or image projecting lens in an image projector.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, and representative devices shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A vibrating device comprising: a dust-screening member which isshaped like a plate as a whole and has at least one side that issymmetric to the X-axis that is a given axis of symmetry; a vibratingmember secured to the dust-screening member and configured to produce,at the dust-screening member, vibration having a vibrational amplitudeperpendicular to a surface of the dust-screening member; and a driveunit configured to drive the vibrating member to produce vibration Z (x,y) at the dust-screening member, the vibration being expressed asfollows:Z(x,y)=W _(mn)(x,y)·cos(γ)+W _(nm)(x,y)·sin(γ) where Z (x, y) isvibration at a given point P (x, y) on the dust-screening member; m andn are positive integers including 0, indicating the order of naturalvibration corresponding to a vibrational mode;${{W_{mn}\left( {x,y} \right)} = {{\sin\left( {{n\;{\pi \cdot x}} + \frac{\pi}{2}}\; \right)} \cdot {\sin\left( {{m\;{\pi \cdot y}} + \frac{\pi}{2}} \right)}}};$${{W_{n\; m}\left( {x,y} \right)} = {{\sin\left( {{m\;{\pi \cdot x}} + \frac{\pi}{2}} \right)} \cdot {\sin\left( {{n\;{\pi \cdot y}} + \frac{\pi}{2}} \right)}}};{and}$γ is +π/4 or ranges from −π/8 to −π/4; and a ratio between a firstbending rigidity along the X-axis of at least the dust-screening memberand vibrating member in the section orthogonal to the X-axis at theintersection of the X- and Y-axes, to a second bending rigidity alongthe Y-axis of at least the dust-screening member in the sectionorthogonal to the Y-axis at the intersection is 0.4 or more, but lessthan 1.0, the Y-axis being orthogonal to the X-axis in a virtualrectangle which has the same area as the surface of the dust-screeningmember, and which has long sides including the one side of thedust-screening member.
 2. The device according to claim 1, wherein γ is+π/4, and the vibration produced at the dust-screening member by thedrive unit is vibration such that peak ridges of the vibration having avibrational amplitude perpendicular to the surface of the dust-screeningmember form closed loops.
 3. The device according to claim 1, wherein γranges from −π/8 to −π/4, and the vibration produced at thedust-screening member by the drive unit is vibration such that peakridges of the vibration having a vibrational amplitude perpendicular tothe surface of the dust-screening member form curves around a midpointof the side which the dust-screening member has.
 4. The device accordingto claim 1, wherein the vibrating member includes a piezoelectricelement, and the drive unit configured to supply a signal to thepiezoelectric element to produce the vibration at the dust-screeningmember, the signal having a frequency that accords with a size andmaterial of the dust-screening member.
 5. The device according to claim4, wherein the drive unit configured to supply a signal to thepiezoelectric element at prescribed time intervals, the signal changingin frequency, from a drive-start frequency to a drive-end frequency inincrements of a given transmutation frequency, including the frequencythat accords with the with size and material of the dust-screeningmember.
 6. The device according to claim 1, wherein a plurality ofvibrating members are provided on the dust-screening member.
 7. Avibrating device comprising: a dust-screening member which is shapedlike a plate as a whole and has at least one side that is symmetric tothe X-axis that is a given axis of symmetry; a vibrating member securedto the dust-screening member and configured to produce, at thedust-screening member, vibration having a vibrational amplitudeperpendicular to a surface of the dust-screening member; and a driveunit configured to drive the vibrating member to produce vibration Z (x,y) at the dust-screening member, the vibration being expressed asfollows:Z(x,y)=W _(mn)(x,y)·cos(γ)+W _(nm)(x,y)·sin(γ) where Z (x, y) isvibration at a given point P (x, y) on the dust-screening member; m andn are positive integers including 0, indicating the order of naturalvibration corresponding to a vibrational mode;${{W_{{mn}\;}\left( {x,y} \right)} = {{\sin\left( {{n\;{\pi \cdot x}} + \frac{\pi}{2}} \right)} \cdot {\sin\left( {{m\;{\pi \cdot y}} + \frac{\pi}{2}} \right)}}};$${{W_{n\; m}\left( {x,y} \right)} = {{\sin\left( {{m\;{\pi \cdot x}} + \frac{\pi}{2}} \right)} \cdot {\sin\left( {{n\;{\pi \cdot y}} + \frac{\pi}{2}} \right)}}};{and}$γ is +π/4 or ranges from −π/8 to −π/4; and a ratio between a firstbending rigidity along the X-axis of at least the dust-screening memberin the section orthogonal to the X-axis at the intersection of the X-and Y-axes, to a second bending rigidity along the Y-axis of at leastthe dust-screening member in the section orthogonal to the Y-axis at theintersection is 0.4 or more, but less than 1.0, the Y-axis beingorthogonal to the X-axis in a virtual rectangle which has the same areaas the surface of the dust-screening member, and which has long sidesincluding the one side of the dust-screening member.
 8. An imageequipment comprising: an image forming element having an image surfaceon which an optical image is formed; a dust-screening member which isshaped like a plate as a whole, has at least one side that is symmetricto the X-axis that is a given axis of symmetry, and has alight-transmitting region at least flaring in a radial direction fromthe center, facing the image surface and spaced therefrom by apredetermined distance; a vibrating member configured to producevibration having an amplitude perpendicular to a surface of thedust-screening member, the vibrating member being provided on thedust-screening member, outside the light-transmitting region throughwhich a light beam forming an optical image on the image surface passes;a sealing structure for surrounding the image forming element and thedust-screening member, thereby providing a closed space in which theimage forming element and the dust-screening member that face eachother; and a drive unit configured to drive the vibrating member toproduce vibration Z (x, y) at the dust-screening member, the vibrationbeing expressed as follows:Z(x,y)=W _(mn)(x,y)·cos(γ)+W _(nm)(x,y)·sin(γ) where Z (x, y) isvibration at a given point P (x, y) on the dust-screening member; m andn are positive integers including 0, indicating the order of naturalvibration corresponding to a vibrational mode;${{W_{m\; n}\left( {x,y} \right)} = {{\sin\left( {{n\;{\pi\; \cdot x}} + \frac{\pi}{2}} \right)} \cdot {\sin\left( {{m\;{\pi\; \cdot y}} + \frac{\pi}{2}}\; \right)}}};$${{W_{n\; m}\left( {x,y} \right)} = {{\sin\left( {{m\;{\pi \cdot x}} + \frac{\pi}{2}} \right)} \cdot {\sin\left( {{n\;{\pi \cdot y}} + \frac{\pi}{2}} \right)}}};{and}$γ is +π/4 or ranges from −π/8 to −π/4, wherein a ratio between a firstbending rigidity along the X-axis of at least the dust-screening memberand vibrating member in the section orthogonal to the X-axis at theintersection of the X- and Y-axes, to a second bending rigidity alongthe Y-axis of at least the dust-screening member in the sectionorthogonal to the Y-axis at the intersection is 0.4 or more, but lessthan 1.0, the Y-axis being orthogonal to the X-axis in a virtualrectangle which has the same area as the surface of the dust-screeningmember, and which has long sides including the one side of thedust-screening member.
 9. The equipment according to claim 8, wherein γis +π/4, and the drive unit produces at the dust-screening membervibration such that peak ridges of the vibration having a vibrationalamplitude perpendicular to the surface of the dust-screening member formclosed loops around an optical axis that passes the image surface of theimage forming element.
 10. The equipment according to claim 9, whereinthe sealing structure includes: a holder arranged so as to achieveairtight sealing between the image forming element and thedust-screening member; and a support member configured to secure thedust-screening member to the holder, the support member being arrangedin a node region that has almost no vibrational amplitude perpendicularto a surface of the dust-screening member.
 11. The equipment accordingto claim 8, wherein when γ is −π/8 to −π/4, and the drive unit producesat the dust-screening member vibration such that peak ridges of thevibration having a vibrational amplitude perpendicular to the surface ofthe dust-screening member form curves surrounding a midpoint of the sidewhich the dust-screening member has.
 12. The equipment according toclaim 11, wherein the sealing structure includes: a holder arranged soas to achieve airtight sealing between the image forming element and thedust-screening member; and a support member configured to secure thedust-screening member to the holder, the support member being arrangedin a node region that has almost no vibrational amplitude perpendicularto a surface of the dust-screening member.
 13. The equipment accordingto claim 8, wherein the vibrating member includes a piezoelectricelement, and the drive unit configured to supply a signal to thepiezoelectric element to produce the vibration at the dust-screeningmember, the signal having a frequency that accords with a size andmaterial of the dust-screening member.
 14. The equipment according toclaim 13, wherein the drive unit configured to supply a signal to thepiezoelectric element at prescribed time intervals, the signal changingin frequency, from a drive-start frequency to a drive-end frequency inincrements of a given transmutation frequency, including the frequencythat accords with the with size and material of the dust-screeningmember.
 15. The equipment according to claim 8, wherein vibratingmembers including the vibrating member are opposed across a transmissionregion of the dust-screening member, through which light passes.
 16. Animage equipment comprising: an image forming element having an imagesurface on which an optical image is formed; a dust-screening memberwhich is shaped like a plate as a whole, has at least one side that issymmetric to the X-axis that is a given axis of symmetry, and has alight-transmitting region at least flaring in a radial direction fromthe center, facing the image surface and spaced therefrom by apredetermined distance; a vibrating member configured to producevibration having an amplitude perpendicular to a surface of thedust-screening member, the vibrating member being provided on thedust-screening member, outside the light-transmitting region throughwhich a light beam forming an optical image on the image surface passes;a sealing structure for surrounding the image forming element and thedust-screening member, thereby providing a closed space in which theimage forming element and the dust-screening member that face eachother; and a drive unit configured to drive the vibrating member toproduce vibration Z (x, y) at the dust-screening member, the vibrationbeing expressed as follows:Z(x,y)=W _(mn)(x,y)·cos(γ)+W _(nm)(x,y)·sin(γ) where Z (x, y) isvibration at a given point P (x, y) on the dust-screening member; m andn are positive integers including 0, indicating the order of naturalvibration corresponding to a vibrational mode;${{W_{{mn}\;}\left( {x,y} \right)} = {{\sin\left( {{n\;{\pi \cdot x}} + \frac{\pi}{2}} \right)} \cdot {\sin\left( {{m\;{\pi \cdot y}} + \frac{\pi}{2}} \right)}}};$${{W_{n\; m}\left( {x,y} \right)} = {{\sin\left( {{m\;{\pi \cdot x}} + \frac{\pi}{2}} \right)} \cdot {\sin\left( {{n\;{\pi \cdot y}} + \frac{\pi}{2}} \right)}}};{and}$γ is +π/4 or ranges from −π/8 to −π/4, wherein a ratio between a firstbending rigidity along the X-axis of at least the dust-screening memberin the section orthogonal to the X-axis at the intersection of the X-and Y-axes, to a second bending rigidity along the Y-axis of at leastthe dust-screening member in the section orthogonal to the Y-axis at theintersection is 0.4 or more, but less than 1.0, the Y-axis beingorthogonal to the X-axis in a virtual rectangle which has the same areaas the surface of the dust-screening member, and which has long sidesincluding the one side of the dust-screening member.